Cytochrome P-450s metabolize xenobiotics such as drugs and carcinogens as well as endobiotics such as steroids and prostaglandins. Multiple forms of enzymes are expressed constitutively or after administration of inducers. A single cytochrome P-450 may metabolize multiple substrates and a single substrate may be acted upon by either a single or several cytochrome P-450s. Cytochrome P-450 may engage normal detoxification or catalyze deleterious carcinogen or mutagen activation. This project has used previously cloned cDNA of two P-450s to construct the two cDNAs into two recombinant viruses, infectious vaccinia and retrovirus. These vectors express the incorporated cDNA into single P-450s when infected into host cells. In both the vaccinia and retrovirus systems, proteins were expressed with the appropriate molecular weights and exhibit enzyme activity typical of each P-450. Studies are in progress to determine the specificity of each expressed protein in the 1) stereochemistry of polycyclic aromatic hydrocarbon metabolism; (2) aflatoxin metabolism; and (3) the metabolism of aminopyrine, antipyrine and theophylline. The results from the above studies indicate a variability of specificity depending on the substrate, and a high degree of specificity for one form of P-450 with some substrates and cross-reactivity for both P-450s with other substrates. In a different project various expression systems are being developed with a large variety of cDNAs and different vectors. Success in this effort will enable us to define the contribution of each of these enzymes to mutagenesis and cell transformation mediated by chemical carcinogens.